The present invention relates generally to a method for removing charge accumulated on a substrate or a sample including an insulator and an apparatus for use with the method, and more particularly to a charge removing method for removing accumulated charge from such a substrate or a sample through light irradiation before and after observing, inspecting, processing or analyzing the same, and an apparatus for use with the method.
Currently, a charged particle apparatus, an SPM (Scanning Probe Microscope) apparatus, a dry etching apparatus, a CVD (Chemical Vapor Deposition) apparatus, and so on are used for observing, inspecting, processing and analyzing LSI, photo masks or the like. For chucking a substrate or a sample in such apparatus, a clamping method, a vacuum chuck, a chuck using static electricity, or the like may be used. The clamping method, however, is not capable of completely chucking a substrate and is susceptible to misalignment during observation, inspection, process, analysis or the like, so that this is not a proper chucking method. Also, since most of such observation, inspection, process and analysis are performed in vacuum, the vacuum chuck is not used. Therefore, chucks using static electricity as shown in JP-A-5-275517 and JP-A-6-120329 are generally used as a chucking method for chucking a substrate or a sample during observation, inspection, process, analysis or the like.
However, when a substrate is chucked by a chuck using static electricity, charge accumulates on the substrate to cause a phenomenon that the substrate is not easily removed from a holder. Another phenomenon observed in this event is that the charge accumulated on the substrate attracts particles.
It is therefore necessary to neutralize charge accumulation due to the charge accumulated on the substrate. Conventionally, a variety of method and apparatus have been proposed for neutralizing charge accumulation on a substrate. For example, JP-A-5-275517 brings a conductor connected to the earth into contact with a substrate to neutralize charge accumulation. Also, JP-A-4-152519, JP-A-1-119668, JP-A-1-243449, and JP-A-57-170526 disclose techniques which irradiate an object under processing with light or ultraviolet rays to neutralize charge accumulated on the object under processing. Particularly, JP-A-4-152519 transports a semiconductor substrate to a separate chamber after it has been processed, and irradiates the substrate with ultraviolet rays to neutralize charge accumulation on the substrate in the separate chamber. On the other hand, JP-A-1-119668, JP-A-1-243449, and JP-A-57-170526 irradiate a substrate with light or ultraviolet rays in a chamber for processing the substrate to neutralize charge accumulation on the substrate.
However, since even the neutralization achieved by the foregoing prior art techniques is not sufficient, charge accumulation does remain partially on a substrate, so that the aforementioned problem is still left unsolved. More specifically, when a substrate or a sample is observed, inspected, processed or analyzed using an electron beam, charge accumulates on the surface of the substrate or the sample, so that when the substrate or the sample is extracted after such operation has been terminated, the accumulated charge attracts particles which end up to attach on the surface of the substrate or the sample. This causes contamination or the like on the surface of the substrate or the sample, thereby adversely affecting the processing in the next step. Effective removal of the accumulated charge as mentioned has been very difficult in the prior art.
It is an object of the present invention to provide a method and apparatus for removing charge through light irradiation so that charge accumulated on a substrate or a sample can be effectively removed in a simple way and with simple means to readily carry the substrate or the sample, and a method and apparatus which use the charge removing techniques.
Difficulties in removing charge accumulated on a substrate or a sample are due to the existence of portions including an insulator within such a substrate or a sample. Therefore, to achieve the above object, the present invention irradiates the substrate or the sample with light at a wavelength which excites electrons in the insulator of the substrate or the sample to produce a photo-conductive effect. Then, a portion of the insulator provided with conductivity through the light irradiation is connected to earth by parts for connecting to earth. In this way, charge accumulated on the insulator is removed from the insulator provided with conductivity through the parts for connecting to earth.